1. Field of the Invention
The present invention relates to a camera which is provided with a flash and in which the size of a photograph frame (hereinafter referred to simply as a frame) can be changed by changing the size of an aperture of the camera.
2. Description of the Related Art
In a known conventional single lens reflex camera, when a flash mode is set, in which a flash of intense light is output, a shutter speed is automatically changed to a speed that is synchronized with the output of the flash. The flash-synchronized shutter speed (hereinafter referred to as synchronized speed, but usually known as an X sync speed) is determined by the time between a point at which the output of the flash is begun and a point at which the output of the flash is ended, and is usually set to a predetermined constant time. When the time for which the shutter is fully open is longer than or equal to the predetermined constant time, light output by the flash illuminates the entire area of the frame to be photographed. Therefore, in a conventional camera, a shutter speed at which the shutter can be held in a fully open position for the predetermined constant time is set as the synchronized speed.
FIG. 1 shows the relationship between an operation of the shutter and an open state of an aperture, wherein the vertical axis denotes the vertical direction of movement of the aperture, and the horizontal axis denotes the time. As shown in the figure, reference numeral 51 shows a movement locus along which a trailing edge of a leading-shutter-curtain is moved, and reference numeral 53 shows a movement locus along which a leading edge of a trailing-shutter-curtain is moved; i.e., these reference numerals 51 and 53 show characteristic lines of movement of the shutter as a whole. Further, reference numeral 61 shows a position of an upper side of a normal aperture (full size), and reference numeral 63 shows a position of a lower side of a normal aperture. An area limited by the leading-shutter-curtain movement characteristic line 51 and the trailing-shutter-curtain movement characteristic line 53 is that within which the aperture is open.
When the shutter speed is indicated by T.sub.A and the fully-open time is indicated by T.sub.C, the fully-open time T.sub.C is a time (t.sub.A -t.sub.X) beginning at a time t.sub.X at which the leading-shutter-curtain movement characteristic line 51 crosses the lower side 63 and ending at a time t.sub.A at which the trailing-shutter-curtain movement characteristic line 53 crosses the upper side 61. Note, a conventional camera is provided with an X contact that is turned ON at the time t.sub.X so that the flash is output in synchronization with a movement of the leading-shutter-curtain, by this ON operation of the X contact.
As described above, in a focal plane shutter, an upper limit of the synchronized speed (i.e., the highest shutter speed) depends upon a time from that at which the leading-shutter-curtain has fully opened the aperture to a time at which the trailing-shutter-curtain begins to close the aperture; i.e., the time for which the shutter is fully open.
Recently, a camera has been developed by which a picture can be taken in a standard frame size and in a panoramic style frame size; this panoramic effect is obtained by reducing the vertical height of the aperture, to thereby form a rectangular frame in which the vertical sides thereof are much shorter than the horizontal sides. Namely, in this camera, the size of aperture can be changed between the standard size and the panoramic style size. When the aperture size is reduced to obtain a panoramic style picture, a space between the upper side 61 and the lower side 63 of the aperture is reduced in FIG. 1. Therefore, a time for which the aperture is fully open is prolonged, even though the same shutter speed is used as that for the standard frame. Note, preferably the synchronized speed is as high as possible when photographing with a daylight synchronized flash, but in a conventional camera the synchronized speed is constant, regardless of the size of the aperture.